1. Field of the Invention
This invention relates generally to a measurement device and, more specifically, to a device and method to measure a gap between two members of a mechanical structure to enable manufacture of a shim for insertion between the two structural members.
2. Background of the Invention
Many mechanical structures are manufactured by forming component parts of the structure followed by an assembly of the parts to produce the structure. During the assembly process, it may be necessary to introduce a shim between the interfacing surfaces of the component parts. A shim is a thin slip or wedge of metal, wood, etc., for placing into crevices, as between machine parts to compensate for wear or to achieve a certain alignment of the parts.
Presently, when the component parts are moved into their final positions, the gaps between the parts are measured using either feeler gauges or capacitive gap measuring instrumentation. The measurement data is sent to a Computer Numerical Control (CNC) machine tool which manufactures the shims. The manufactured shims are then installed, and final “pull-up” tolerances are checked before the mating components are finally fastened together.
The present method becomes impractical when applied to composite aircraft. This is especially true for composite aircraft having any of the following characteristics: a large quantity of shims need to be produced; the shims have a large surface area; shim materials are difficult to machine such as composites, titanium, and the like; denser data collection requirements such as tighter pull-up tolerances, mating surfaces are not necessarily planar, unknown level of allowable surface distortion, and the like; and measurement access is difficult for the mechanic to access.
The above requirements make the manual measurement of gap data impractical. The fact that the measurement must take place after the components are in place means that even with CNC machines installed on the final integration floor, there will be at least four hours “dead time” during final integration.
Furthermore, in present devices and methods, only one sensor is used. This sensor is manually positioned and individual data points are collected. This becomes impractical when a large number of points must be collected, due to the manual labor required as well as the difficulty in accurately positioning the sensor.
Clearly, there is large benefit in improving gap measurement and accuracy. There is an even greater benefit in allowing the measurement to take place before final systems integration takes place. This would allow the appropriate shims to be manufactured in advance. This would eliminate the “dead time” and “Just-In-Time” shim manufacturing requirements. It would also reduce process flow and allow shim manufacturing operations to be moved to a remote site.
Therefore, a need exists for a system and method that overcomes the problems associated with the prior art.